[PATCH] D13655: DAGCombiner: Combine extract_vector_elt from build_vector

[Simon Pilgrim via llvm-commits]

RKSimon added a subscriber: RKSimon.
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RKSimon added a comment.

Very surprising that this was missing!


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Comment at: include/llvm/Target/TargetLowering.h:1723
@@ -1722,1 +1722,3 @@
 
+  // Return true if it is profitable to use a scalar input to a BUILD_VECTOR
+  // even if the vector itself has multiple uses.
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By 'use' do you just mean 'directly access' or do you foresee other possibilities?

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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:11893
@@ +11892,3 @@
+       TLI.aggressivelyPreferBuildVectorSources(VT))) {
+    return InVec.getOperand(ConstEltNo->getZExtValue());
+  }
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You may need to confirm that the operand value type is the same as the BUILD_VECTOR scalar value type - implicit truncation may be occurring.


http://reviews.llvm.org/D13655